Estimating the Sedimentation Coefficient in Shafaroud Watershed of Guilan

The functional effects of each of the components of a Watershed can be seen and evaluated in the intensity of its erosion and produced sediments. Usually, in any basin, as a result of the eroded materials in the basin due to natural sedimentary traps, the amount of erosion is more than that of the sediment. Therefore it is necessary to detemine the relationship between sedimentation coefficient and physical parameters of any basin so as to be able to execute the required plans and management policies. So, by recognizing the effective factors in basins sedimentation coefficient, the appropirate strategy of sediments control can be formulated with more precision. In this study, to determine the coefficient of sedimetion, Shafaroud basin was divided into six subbasins on the basis of the topographic map (1:5000) and the amounts of soil erosion and sedimentation class were computed using MPSIAC model. According to the above method, the annual sedimentation amount was computed as m3/km2 855/50. Besides, the annual volume of the sediments entering into the dam from the total area of the basin amounts to m3 0.16. To calculate the turbidity coefficient in Shafaroud Basin, thespecific sediment value of t/y/km2 556/3 and the specific debi value of lit/s/km2 296/3 were used and so the coefficient was obtained as kg/m3 0.06.Results indicated that there was a negative ralationship between the area of the basin and the sedimentation coefficient (r=-0.98). The correlation between the gradient and the erosion coefficient was positive (r=0.86). Average amount of the sedimentation coefficient in this area was %77. The applied method has been measured and campared with other methods of erosion evaluation.